This disclosure is intended to teach by way of example and not by way of limitation.
The present invention pertains to the fields of polymer chemistry and specialty chemicals. In particular, this invention relates to the production of salt derivatives of 5-sulfoisophthalic acid. Historically, salt derivatives of sulfoisophthalic acid, such as the mono-lithium and mono-sodium salts of 5-sulfoisophthalic acid, are used in the production of dyed nylon fibers among other polymer fibers. More recently, there has been considerable research devoted to developing new salts of 5-sulfoisophthalic acid and exploring their chemical behaviors and potential uses. This application is an example of such research and development.
A short description of the use of known salt derivatives of 5-sulfoisophthalic acid in nylon processes is presented to provide some context for the research and discoveries that underlie the invention.
Many types of nylons exist and are usually differentiated based on the components used to make them. For example, “nylon 6-6” is a term used to identify nylon made by reacting hexamethylene diamine and adipic acid. Both components donate 6 carbons to the polymer chain thus the nylon is designated “6-6”.
Nylon fibers, especially those used for carpet fiber, are also classified as to type, depending on the fiber's receptivity to acid dyes and basic or cationic dyes. Cationic dyeable nylon fibers generally exhibit inherent stain resistant properties as compared to other nylon types but traditionally suffered from poorer lightfastness, especially in light shades. This resulted in the under-utilization of cationic dyeable nylon as a carpet fiber. As expected, considerable time, energy, and resources were devoted to finding new and improved methods to enhance the dye absorbing characteristics of cationic dyeable nylon. Over the years, several methods were developed in which very specialized chemicals were added to the fiber production process to impart improved cationic dye-ability to the polymer.
Two such specialized chemicals are the lithium and sodium salts of 5-sulfoisophthalic acid, commonly known as LiSIPA and NaSIPA respectively. It is believed that other metal salts of SIPA may have similar applications or even more valuable applications.
Developing a commercially viable method of manufacture for SIPA salts presents several challenges, one of which is the variability in HSIPA chemistry. As mentioned previously, the lithium and sodium salts of HSIPA are well known in the art. However, HSIPA chemistry is such that one cannot necessarily take a known process for making one salt (e.g., LiSIPA), switch out the metal (e.g., switch to Na), and expect that the process will result in a similar salt product. For example, one can wash a crude NaSIPA product with water but doing the same with LiSIPA will result in lost product. Likewise, washing crude LiSIPA with acetic acid results in a hydrate or anhydrous product whereas washing crude NaSIPA with acetic acid results in a solvate. Also, one metal cation may require a different solvent system than another metal cation
In addition, many of the known processes for producing HSIPA salts results in product having high sulfate levels. A high sulfate HSIPA salt can cause problems in polymer processes. For example, LiSIPA salts with accompanying high levels of sulfate are associated with high levels of nylon filament breakage due to sulfate precipitation. Accordingly, HSIPA salts with a low-sulfate composition are of value because they are expected to cause fewer problems in polymer production processes.
Due to these and other problems in the prior art, some of which are disclosed herein, there is a general need for new technology in the arena of salt derivatives of SIPA. There is a need for new salt derivatives that may have improved polymer processing characteristics as compared to known salts. There is a need to produce such salts in a manner that is both efficient and results in low sulfate levels in anticipation of possible use in nylon applications. There is a need for a robust platform process to produce such salts that can be used to manufacture several different types of salts. Furthermore, the process should be suitable for commercialization using equipment currently employed in most SIPA manufacturing processes.